The invention relates to fabricating parts of complex shape out of composite material.
An example of an application of the invention is fabricating parts out of thermostructural composite material for use in the fields of aviation and space.
In well-known manner, fabricating a part out of thermostructural composite material comprises making a fiber preform out of refractory fibers (carbon fibers or ceramic fibers), the preform having a shape that is close to the shape of the part that is to be fabricated, and then densifying the fiber preform with a refractory matrix (of carbon or ceramic).
In order to make the fiber preform, various textile techniques can be used. One known technique consists in making a preform by three-dimensional weaving, or multilayer weaving. Such a method of weaving enables interlacing to be established between layers of yarns so as to give the preform the strength needed to obtain a composite material part having high-grade mechanical properties.
With parts that are complex in shape, it can be difficult or even impossible to make a fiber preform directly by three-dimensional (3D) weaving.
It is then possible to make the fiber preform as a plurality of separate parts that are assembled together, e.g. by stitching or by implanting yarns, prior to densifying the preform. However the connections between the various portions of the preform may constitute points of weakness.
It is also known to make a fiber blank by 3D weaving with the fiber preform being obtained from the blank by shaping the blank. The shaping of the blank may comprise unfolding or folding over one or more portions of the blank that are adjacent to de-bonding zones that are formed during weaving or that are adjacent to cuts or incisions that are made in the blank.
The fiber preform is held in the desired shape by consolidation using a liquid technique or a gaseous technique. Liquid consolidation comprises impregnating the preform with a consolidation composition containing a resin and applying heat treatment to cure and pyrolyze the resin. The quantity of resin is selected so that the pyrolysis residue achieves sufficient densification to enable the preform to conserve its shape without the assistance of support tooling. Gas consolidation comprises partially densifying the preform by depositing a material on the fibers by chemical vapor infiltration (CVI), the quantity of material that is deposited being selected to be sufficient to connect together the fibers of the preform so that it conserves its shape without the assistance of support tooling. The consolidated preform is subsequently densified with a refractory matrix.
Document U.S. Pat. No. 5,350,545 describes a method of making ceramic matrix composite (CMC) parts of complex shape by using a ceramic-precursor resin to consolidate a fiber preform made of a woven or braided material, followed by densifying the consolidated preform by chemical vapor infiltration.
In addition, particularly but not exclusively for CMC materials, the formation of an interphase on the fibers serves, when using liquid consolidation, to avoid the residue of pyrolyzing the resin adhering excessively strongly on the fibers, and also serves, when using gas consolidation, to greatly reduce sensitivity to cracking and to increase ability to withstand impacts.
Furthermore, it may be desirable, particularly when the fibers used are commercially available ceramic fibers, to perform treatment on the fibers prior to forming an interphase and consolidation, for the purpose of eliminating a sizing or an oxide film present on the surfaces of the fibers.
Those various operations require a great deal of manipulation, thereby increasing the complexity and the cost of fabricating parts.
Document WO 97/33829 discloses a method of fabricating valves out of carbon/carbon composite material, the method including making a braided preform. A continuous braid may be made with carbon inserts being put into place at regular intervals inside the braid in order to obtain valve preforms by cutting out segments from the braid containing the inserts.